Apparatus for ageing alkali cellulose



April 5, 1966 K. FRIDAY ETAL 3,244,487

APPARATUS FOR AGEING ALKALI CELLULOSE origin-a1 Filed Feb. 2, 1960United States Patent C) 3,244,487 APPARATUS FR AGEHNG ALKALI CELLULGSEKeith Priday, deceased, late of Coventry, England, by

Agnes Priday, Coventry, and Sidney Walter Clarence Friday, Gloucester,England, executors, and John Walter More, Kenilworth, England, assignorsto Courtaulds Limited, London, England, a British company Originalapplication Feb. 2, 1960, Ser. No. 6,289. Divided and this applicationDec. 18, 1964, Ser. No. 428,000 Claims priority, application GreatBritain, Feb. 12, 1959,

4,901/59 2 Claims. (Cl. 23-283) This application is a division of ourcopending application Serial No. 6,289, led February 2, 1960, nowabandoned.

This invention concerns the ageing of alkali cellulose and provides anapparatus suitable for that purpose.

In the production of viscose ,the alkali cellulose obtained bysubjecting cellulose to treatment with alkali is usually left to age fora period before subsequent xanthation. It has already been proposed tocarry out the ageing by introducing the alkali cellulose at the top of avertical tower and allowing the resulting mass of alkali cellulose topass slowly down the height of the tower by removing alkali cellulosecontinuously or intermittently from the bottom of the tower. In thisway, it may be ensured that the material uniformly takes a predeterminedtime in passing down the tower.

It is a known fact that the total depth of the mass of alkali cellulosein the tower is limited by factors other than the desired ageing time. Adepth is reached beyond which no further ageing takes place.

The throughput of alkali cellulose in plants of this type can beincreased by providing a further ageing tower or extending thedimensions of the tower laterally. In either case, additionalfloor-space must be available and further equipment must be provided forsupplying alkali cellulose to the second tower or to the laterallyextended upper end of the rst tower.

We therefore have devised a process for affording a greater throughputper unit of cross-sectional area and an apparatus for carrying out thatprocess.

According to the present invention, a process for ageing alkalicellulose comprises supplying alkali cellulose to the upper end of avessel of uniform horizontal cross-section, allowing the alkalicellulose to pass down at least one part of the height of the vessel ata controlled rate by maintaining a mass of alkali cellulose in that partand continuously or intermittently removing alkali cellulose in discretefragments from the lower face of the mass, bringing the removed alkalicellulose into contact with oxygen, e.g. in the form of anoxygen-containing gas, and thereafter allowing the alkali cellulose topass down at least one further part of the height of the vessel at acontrolled rate by maintaining a mass of alkali cellulose in that partand continuously or intermittently removing alkali cellulose in discretefragments from the lower face of that mass.

The temperature of the alkali cellulose within the vessel is maintainedsubstantially constant during the ageing. For example, a jacket may beprovided which envelops the vessel and in which fluid may be circulated.A preferred method of controlling said temperature is by controlling thetemperature at which the earlier step comprising steeping the cellulosein aqueous alkali is carried out. The vessel may then be lagged toreduce heat losses, the temperature being maintained in the vessel bythe heat of reaction.

3,244,487 Patented Apr. 5, 1966 The alkali cellulose may be brought intocontact with oxygen or an oxygen-containing gas after each ageing stageexcept the last, either by positively introducing the gas, c g. air, or(less satisfactorily) by merely allowing ingress of air through one ormore inlets or ports. A typical rate of flow for a positively-introducedair supply would be of the general order of 6 cu. ft./min. The gas may,if desired, be warm and/or humidied.

Apparatus according to the present invention for ageing alkali cellulosecomprises a tower of uniform crosssection having a feed opening adjacentits upper end and a discharge opening adjacent its lower end, at leastone extractor mechanism transversely disposed between the ends of thetower for removing discrete fragments of any alkali cellulose whichcomes into contact with the upper surface of said mechanism, a linalextractor mechanism transversely disposed across the discharge openingfor removing discrete fragments of any alkali cellulose which comes intocontact with the upper surface of said final extractor mechanism, and agas inlet below each of the extractor mechanisms except the finalextractor mechamsm.

Any or all of the extractor mechanisms may comprise a plurality ofparallel rotary shafts, each carrying a plurality of pickers. Thepickers may be in the form, for example, of rods or of toothed discs. Afurther form is described hereafter by reference to the accompanyingdrawing.

lf desired, the alkali cellulose supplied to the upper end of the towermay be distributed over the surface of the upper mass. For example, aconveyor or a system of batlles may be employed for this purpose. Thedischarge of the aged alkali cellulose may be eifected via a hopperbel-ow the final extractor mechanism and/ or by means of a conveyor.

The invention will now be further described by reference to theaccompanying drawing, which represents in longitudinal section apparatusaccording to the invention.

In the drawing, a tower 1 is provided adjacent its middle and bottomrespectively with transverse extractor mechanisms 2 and 3. Each of thelatter comprises a number of extraction rolls consisting of shafts 2a or3a disposed in parallel across the width of the tower and carryingpicker lingers 2b and 3b in the form of slats parallel to, andprojecting radially from, the shafts. The extraction rolls are rotatedintermittently during Operation.

Below the rst extractor mechanism 2, a duct 4 encircles the tower,communication between the duct and the interior of the tower beingprovided Iby inlet ports 5. The ports 5 yare yshielded by baille 6, ofwhich, for the sake of clarity, only two are shown in the drawing.

Steeped and shredded alkali cellulose is supplied to the tower via achute 7, whence it drops into a spreader 8. The spreader 8 comprises areversible conveyor belt 9, mounted upon a carriage 10. The carriage 10reciprocates between two positions in which it lies directly above theopposite ends of the interior of the tower. From the position shown inthe drawing the carriage 10 moves to the right, while the belt 9 isdriven in a clockwise direction. When the carriage 10 is directly abovethe righthand end of the tower interior, the carriage 10 begins to -moveback toward the position shown. Simultaneously, the belt 9 reverses. Bymeans of the spreader 8, alkali cellulose is distributed uniformly overthe cross-section of the tower 1.

During operation of `the tower, a mass of alkali cellulose is built upabove each of the extractor mechanisms and the rate of feed of freshalkali cellulose and rate of intermittent rotation of the extractionrolls are controlled so as to maintain constant the depth of the eachmass. By varying these rates together, it is possible to vary the lengthof time during which the crumbs of alkali cellulose are retained in eachzone of the tower.

After passing through the rst extractor mechanism 2, the alkalicellulose is subjected to aeration by contact with a slow current of airintroduced via an air supply pipe 11, the duct 4, and the ports 5. Thebaffles 6 prevent crumbs of alkali cellulose entering the ports andpossibly blocking the ports or duct as a result.

The alkali cellulose subsequently passes down the sec,- ond mass and isremoved from the -bottom of that mass by the second extractor mechanism3, whence it is collected by a conveyor 12 and taken to the next stageof the viscose preparation process.

Within the scope of the invention, the shape and dimensions of the towermay be varied between fairly wide limits. Since, however, the maximumwidth of the tower is limited by the length of extraction rollsavailable, it is preferred that the tower be rectangular incross-section. A typical tower is 9 feet wide, 30 feet long and 18 feettall. In this latter tower, the depth of alkali cellulose in each masscould conveniently be about 6 feet. The total retention time of alkalicellulose in the tower could then be of the order of 13 hours. It is, ofcourse, possible in a taller tower to provide more than one intermediateextractor mechanism with associated aeration means.

The extraction rolls may rotate intermittently and through only aportion of a revolution each time they move, or continuously. Forexample, they may rotate through one fth of a revolution each time, theoverall speed being of the order o f 1 revolution every 10 minutes, forexample.

It will be appreciated that the present invention not only provides amethod of making use of the upper regions of a tower of heightsubstantially greater than the maximum possible alkali cellulose depth,but simultaneously provides `an apparatus which can accept a greaterthroughput per unit of cross-sectional area than that posisible with theageing towers hitherto used.

What is claimed is:

1. Apparatus for ageing alkali cellulose comprising a tower of uniformcross-section, a feed opening adjacent the upper end of the tower, acarriage adapted to reciprocate across the feed opening, a reversibleconveyor supported by the carriage, a discharge opening adjacent thelower end of the tower, at least one extractor disposed between the endsof the tower, a nal extractor across the discharge opening, each ofwhich extractors comprises a plurality of parallel transverse rotaryshafts each carrying a plurality of pickers, and a gas inlet fromoutside the tower below each extractor except the final extractor,whereby external gas is introduced into the tower.

2. Apparatus for ageing alkali lCellulose comprising a tower of uniformcrossasection, a feed opening adjacent the upper end of the tower, acarriage adapted to repricocate across the feed opening, a reversibleconveyor supported by the carriage, a discharge opening adjacent thelower end of the tower, at least one extractor disposed between the endsof the tower, a iinal extractor across the discharge opening, each ofwhich extractors comprises a plurality of parallel transverse rotaryshafts each carrying a plurality of pickers, a gas duct substantiallyencircling the tower below each extractor except the final extractor anda plurality of inlets from outside the tower connecting each duct withthe interior of the tower, whereby external gas `is introduced into thetower.

References Cited by the Examiner UNITED STATES PATENTS 2,499,097 12/1949Seaman et al. 23--283 X 3,051,560 8/1962 Barboza 23-284 FOREIGN PATENTS1,039,476 5,/1953 France.

MORRIS O. WOLK, Primary Examiner.

JAMES H. TAYMAN, JR., Examiner.

1. APPARATUS FOR AGEING ALKALI CELLULOSE COMPRISING A TOWER OF UNIFORMCROSS-SECTION, A FEED OPENING ADJACENT THE UPPER END OF THE TOWER, ACARRIAGE ADAPTED TO RECIPROCATE ACROSS THE FEED OPENING, A REVERSIBLECONVEYOR SUPPORTED BY THE CARRIAGE, A DISCHARGE OPENING ADJACENT THELOWER END OF THE TOWER, AT LEAST ONE EXTRACTOR DISPOSED BETWEEN THE ENDSOF THE TOWER, A FINAL EXTRACTOR ACROSS THE DISCHARGE OPENING, EACH OFWHICH EXTRACTORS COMPRISES A PLURALITY OF PARLLEL TRANSVERSE ROTARYSHAFTS EACH CARRYING A PLURALITY OF PICKERS, AND A GAS INLET FROMOUTSIDE THE TOWER BELOW EACH EXTRACTOR EXCEPT THE FINAL EXTRACTOR,WHEREBY EXTERNAL GAS IS INTRODUCED INTO THE TOWER.